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SECTION 4
SERVICING
INFORMATION
4.1 INTRODUCTION
This section contains information
necessary to maintain,
calibrate and troubleshoot the Model 602 Electrometer.
WARNING
The procedures
described
in this section
ere for use only by qualified
service person-
nel.
Do
not
perform
these
procedures
unless qualified
to do so. Many of the steps
covered in this section may expose the indi-
vidual
to potentially
lethal
voltages
that
could
result in personal
injury
or death if
normal
safety
precautions
are not
ob-
served.
4.2 CALIBRATION
The calibration information provided is a method of checking
the Model 602 to make sure it operates properly and within
specification. See the specifications that precede Section 1.
4.2.1 Recommended
Equipment
Recommeded calibration equipment is listed in Table 4-l.
Alternate test equipment may be used as long as equipment
accuracy is et least as good as the specifications listed in
Table 4-1.
NOTE
Unless
otherwise
stated,
all the following
calibration
procedures will be made with the
FEEDBACK switch set to NORMAL and the
IV-1MA switch set to 1V.
4.2.2 Calibration
Schedule
1. Check offset current (paragraph 4.7) at regular intervals to
make sure the input transistors are functioning
correctly.
2. Verify the value of the high megohm resistors (paragraph
4.9) approximately every six months.
3. Calibrate the meter zero (paragraph 4.4) about once a year
or when components are replaced.
4. Check the Model 602 accuracy (paragraph 4.10) once a
year, after adjustment,
or if improper
operation
is
suspected.
4.3 PRELIMINARY
PROCEDURES
Battery
Check-Check
the condition of the batteries as
outlined in paragraph 2.5 and Table 2-2.
Zero Balance-Set
the Model 602 to the 1OV range and turn
the instrument on. Set the ZERO CHECK button to lock.
1. If the unit is operative, the meter should be on scale + or -.
Zero the meter with the COARSE, MEDIUM, and FINE
controls. Increase the voltage sensitivity in steps to the
1mV range by advancing the multiplier switch. Zero the
instrument on each range.
2. If the instrument is inoperative (meter pinned, etc.) check
error
in
setup
end
obvious
problems
before
troubleshooting.
Isolation
Check-Set
up the test circuit in Figure 4-1.
Disconnect the shorting link from CASE to LO. Set the Model
480 to the 1OnA range and zero check. Program the Model
230 to output 1OOV. Take the Model 480 out of zero check.
The Reading on the Model 480 should be less than WA
IlOnA). Usina Ohms law calculate the isolation resistance.
For example:-R = E/I = lOOV/lO-aA= 1O"'D.
Table 4-l. Recommended
Test Equipment
Item
Description
Specification
Mfg.
Model
A
DMM
lpV-1ooov
Keithley
195
B
Voltage Source
1oov
Keithley
230
C
Picoammeter
10.9A sensitivity
Keithley
480
0
RMS Voltmeter
-
H-P
3400A
E
Chart Recorder
-
H-P
70358
F
Null Detector
1OOpV Null Resolution
Keithley
165
G
Current Source
lo-5A to 10.'A f0.2%
Keithley
220
H
10-W Resistor
1O"D +2%
Keithley
R-289-10"
I
Signal Generator
-
H-P
200CD
J
AC Voltmeter
K
1OW Resistor
low
+2%
H-P
400F
Keithley
R-289-10"'
L
109R Resistor
low
*29/o
Keithley
R-289-109
M
1WD Resistor
l@D *2%
Keithley
R-289-108
4-l
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